I believe that mass balancing would improve the situation - it would probably solve it all together! But who wants to add lead to an aircraft?
as it turns out, I think most people are ending up slightly nose heavy with a YS 110 up front, so this might not be a bad idea.. I however have an OS 91FX which is a little lighter and it balances right on the money.

I had a thought that possibly the elevators could be stretched to make the chord about 5 - 10 mm longer. This should improve the flutter situation allowing more airflow over the tail, behind the hinge point. I have read about jet pilots moving the hinge point on all moving control surfaces to eliminate tail flutter.

The other suggestion is that the trailing edge of the elevators should be rounded not square like they are. Isn't this creating unnecessary turbulance?

I don't know if these suggestions would make any difference, I design Highways for a living, not aircraft! (only during my lunchbreaks!)

Alvin, Do the new Synergy kits come with sheet balsa Stabs and Elevators? or are the elevators still built up like the original kit? I Notice on Swill's Synergy, it was the elevator that failed - the stab seems to be ok.